Diamonds are weighted to the thousandth (.001) of a carat and then rounded to the nearest hundredth (.01). The stone will only be rounded up to the nearest hundredth if the thousandth digit is a 9. For example, a stone that weights 1.768 cts. would be rounded to 1.76 cts., but one that weights 1.769 cts. would be rounded to 1.77 cts.